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Ecology of the Shortgrass SteppeA Long-Term Perspective$
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W. K. Lauenroth and I. C. Burke

Print publication date: 2008

Print ISBN-13: 9780195135824

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195135824.001.0001

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Trophic Structure and Nutrient Dynamics of the Belowground Food Web within the Rhizosphere of the Shortgrass Steppe

Trophic Structure and Nutrient Dynamics of the Belowground Food Web within the Rhizosphere of the Shortgrass Steppe

(p.248) 11 Trophic Structure and Nutrient Dynamics of the Belowground Food Web within the Rhizosphere of the Shortgrass Steppe
Ecology of the Shortgrass Steppe

John C. Moore

Jill Sipes

Oxford University Press

Belowground organisms are key components of the trophic structure and they mediate the dynamics of nutrients of all terrestrial ecosystems. The interactions among assemblages of belowground microorganisms and their consumers mediate the cycling of plant-limiting nutrients, influence aboveground plant productivity, affect the course of plant community development, and affect the dynamic stability of aboveground communities following natural and anthropogenic disturbances (Clarholm, 1985; Ingham et al., 1985; Laakso and Setälä, 1999; Naeem et al., 1994; Tilman et al., 1996; Wall and Moore, 1999). The influence of belowground organisms on the aboveground plant community is heightened in systems such as the shortgrass steppe (Blair et al., 2000), given the relatively high percentage of plant production that is diverted belowground through plant roots. Many of the human-induced changes that the shortgrass steppe has been subjected to during the past 150 years fall outside the scope of the natural variations in climate and grazing. This conflict between the natural history of the shortgrass steppe and the more recent human legacy forms the backdrop of this chapter. First we present a detailed description of the belowground food web for the native shortgrass steppe and present its structure in terms of the patterns of trophic interactions, the distribution of biomass, the flow of energy, and the strengths of interactions. Second, we explore how three disturbances—managed grazing, agricultural practices, and climate change (altered precipitation and temperature, and elevated CO2)—have altered the structure of the belowground community. We conclude with a synthesis of the common patterns that we observed in the grassland’s response to these disturbances, and speculate on their consequences. Aboveground plant parts provide from 20% to 40% cover with exposed soil between them (Lauenroth and Milchunas, 1991). Much of the aboveground production remains in place as standing dead, rather than falling to the soil surface as litter. The ratio of shoot production to root production is roughly 1:1, contrasting sharply with forests, where far more production is allocated aboveground (Jackson et al., 1996; Milchunas and Lauenroth, 1993, 2000). Hence, in the shortgrass steppe, plant roots provide the major input of carbon to soil. As such, plant roots are the focal point of biological activity in soils (Coleman et al., 1983).

Keywords:   Carbon flow, Energy flow food web, Functional food web, IBP Grassland Biome project, Permafrost, Rhizosphere, Soil organic carbon, Thunderstorms, Tillage of soil

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